System and method for utilizing rainwater collected at buildings

ABSTRACT

A system for making use of rainwater falling on houses and buildings, which comprises a means for removing a predetermined quantity of initial precipitation from the rainwater collected form the roof surface of the building; and a purifier receiving the subsequent rainwater from which the initial precipitation has been removed. The purifier includes a filtering tank, a sterilization tank, and a supply tank connected to the sterilization tank. The filtering tank has a physical filter and a pH adjusting agent, the sterilization tank contains a primary reactive catalyst for producing active oxygen species, and the supply tank supplies aqueous hydrogen peroxide to the primary reactive catalyst. The system also has a storage tank that stores the purified rainwater supplied from the purifier. The storage tank contains a secondary reactive catalyst for decomposing and eliminating residual active oxygen species remaining in the purified rainwater supplied from the purifier.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a divisional of application Ser. No.09/842,378, filed Apr. 25, 2001, the disclosure of which is incorporatedby reference in its entirety

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a system and a method for makinguse of rainwater falling on and collected at houses and buildings.

[0004] 2. Description of the Related Art

[0005] In general, the volume content or the filling ratio of watermolecules in water is at most about 34%. To this end, water is comparedto sponge having a number of air gaps ill it. Since water molecules arechemical compounds consisting of oxygen and hydrogen, they attract bothcations (positive ions) and anions (negative ions)) and trap varioussubstances in the gaps among the water molecules.

[0006] Water is categorized as a solvent with a property of dissolvingmaterials very well. On the other hand, most materials existing on theearth are categorized as solutes that are soluble in water. As commonlyunderstood, “water”, including the tap water, is a mixture of solvent(i.e., a gathering of water molecules) and solutes, such as minerals.

[0007] “Pure water” is artificial water, which is produced by physicallyfiltering water, i.e., a mixture of water molecules and various solutes,and removing such solutes and impurities. Pure water has a highabsorbency, which is an essential element of its function as a solvent.Pure water is called “hungry water” because of its absorbency, and isused to rinse IC substrates because of its cleansing ability. Pure wateris also used as a raw material for drinking water and various beveragesbecause it contains few impurities or solutes. Thus, pure water has beenbroadly applied to various uses in these years.

[0008] While pure water is an artificially filtrated product, rain andsnow are products of the nature and closest to pure water because theyare gatherings of pure water molecules evaporating in the atmosphere.

[0009] The quantity of solutes contained in a unit volume of water isexpressed as hardness. The hardness of tap water in Japan is about 70 mgto 170 mg per liter, and is categorized as soft water containing fewsolutes by global standards. The hardness of tap water in mountainousareas of Europe is about 370 mg to 400 mg per liter, and is categorizedas hard water. The hardness of rainwater is much lower even than softwater, at less than 20 mg per liter. This means that rainwater issupersoft water containing little solute and extremely close to thegathering just of water molecules that is, pure water.

[0010] The less solutes contained in water, the easier it is to filtrateor purify, and the more possible to treat without using harmful chlorineor other chemicals. Accordingly, rainwater can be recycled into safenatural water. Such recycled rainwater is superior in absorbency, andhas a broad range of uses, including rinsing water or drinking water. Aslong as a reliable filtering means is used and the quality of rainwateris guaranteed, rainwater can be optimally used in various ways,including watering garden plants, washing cars, sanitary water, kitchenwater and drinking water.

[0011] However, with the conventional techniques, rainwater has not beenpositively or practically utilized, in spite of its superior nature andpossibility as the optimum living water. So far, rainwater has only beentreated as wastewater, and recycling of rainwater has not beenconsidered sufficiently.

SUMMARY OF THE INVENTION

[0012] Therefore, it is one of the objectives of the present inventionto reevaluate the properties of rainwater, and to provide a system and amethod that can positively utilize rainwater collected at houses andbuildings, making the best use of this natural resource.

[0013] To achieve the objective, rainwater is collected form the roofsurface of a building or a house through a gutter. A predeterminedamount of initial precipitation is removed or thrown away, and thesubsequent rainwater is treated (e.g., purified) and stored in a storagetank. The purification includes pH adjustment and sterilization of therainwater. The stored rainwater is then taken out of the storage tankby, for example, pumping for actual use.

[0014] In another method of utilizing rainwater, rainwater is collectedfrom the roof surface of a building or house through a gutter. Apredetermined amount of initial precipitation is removed or thrown away,and the subsequent rainwater is supplied to a purifier, in which therainwater is subjected to pH adjustment and sterilization. The purifiedrainwater is supplied to a storage tank. The water level of the storagetank is monitored, and if the water level reaches the prescribed upperlimit, the rainwater is prevented from entering the purifier or thestorage tank.

[0015] In still another method of utilizing rainwater, rainwater iscollected from the roof surface of a building through a gutter. Apredetermined amount of initial precipitation is removed or thrown away,and the subsequent rainwater is supplied to a purifier, in which therainwater is subjected to pH adjustment and sterilization. The purifiedrainwater is then supplied to a storage tank. The water level of thestorage tank is monitored, and if the water level reaches the prescribedlower limit, a predetermined amount of tap water is supplied to thestorage tank in order to keep the water level at a certain level.

[0016] The second and third methods may be combined. In this case, thosesteps up to the supplying the purified rainwater in the storage tank arethe same. Both the upper and the lower limits of water level of thestorage tank are monitored. If the water level reaches the prescribedupper limit, no more rainwater is supplied to the purifier or thestorage tank, and if the water level reaches the prescribed lower limit,a predetermined amount of tap water is supplied to the storage tank.

[0017] In any one of the above-described methods, rainwater is subjectedto a prescribed physical filtration at or before the inlet port of thepurifier. The purification step includes neutralization of acidrainwater by, for example, pH-adjustment, and sterilization using activeoxygen species (or free radicals) produced by decomposition of aqueoushydrogen peroxide.

[0018] Preferably, the residual active oxygen species remaining in thepurified rainwater is decomposed or eliminated in the storage tankusing, for example, secondary reactive catalyst.

[0019] Preferably, before the purified rainwater is supplied from thestorage tank for indoor use, an active charcoal filter and a sedimentfilter further filter the purified rainwater.

[0020] In another aspect of the invention, a system for utilizingrainwater falling on buildings and houses is provided. The systemcomprises a means for removing a predetermined amount of initialprecipitation from rainwater collected from the roof of a buildingthrough a gutter, a purifier including a filter and a sterilizer, and astorage tank for storing the purified rainwater. The purifier receivesrainwater, from which the initial precipitation has been removed. Thefilter of the purifier filters the rainwater physically, and adjusts thepH value of the filtered rainwater. The sterilizer sterilizes thefiltered and pH-adjusted rainwater using active oxygen species (i.e.,free radicals) produced by decomposition of aqueous hydrogen peroxide.

[0021] Another type of rainwater utilization system comprises an initialprecipitation collection tank, a purifier including a filter and asterilizer, a switching valve, a storage tank for storing purifiedrainwater, and a level sensor for sensing the water level of the storagetank. The initial precipitation collecting tank temporarily stores apredetermined amount of initial precipitation of the collecting from theroof of the building. The filter of the purifier carries out physicalfiltration and pH adjustment, and the sterilizer sterilizes the filteredand pH-adjusted rainwater using active oxygen species (i.e., freeradicals). The switching valve switches the water path between theinitial precipitation collection tank and the purifier. To be moreprecise, if the water level of the initial precipitation collection tankreaches a predetermined level, the switching valve closes up so that nomore rainwater flows into the initial precipitation collection tank, andinstead, that the subsequent rainwater flows into the purifier. Thelevel sensor provided to detect the water level of the storage tank isconnected to and cooperates with the switching valve. If the levelsensor detects that the water level of the storage tank has reached theupper limit, it causes the switching valve to switch the water path andguide the rainwater into the initial precipitation collection tank.

[0022] Still another type of rainwater utilization system comprises aninitial precipitation collection tank, a purifier, a storage tankstoring purified rainwater, a tap-water supply pipe equipped with atap-water supply valve, and a level sensor for sensing the water levelof the storage tank. The initial precipitation collection tanktemporarily stores a predetermined initial amount of rainwater collectedfrom the roof of a building through a gutter. The purifier receives thesubsequent rainwater after the initial precipitation has been removedinto the initial precipitation collection tank. The filter of thepurifier carries out physical filtration and pH adjustment, and thesterilizer sterilizes the filtered rainwater using active oxygen species(i.e., free radicals). The level sensor is connected to and cooperateswith the tap-water supply valve. If the level sensor detects the waterlevel of the storage tank having reached the prescribed lower limit, itcauses the tap-water supply valve to open in order to supply apredetermined amount of tap water into the storage tank.

[0023] Still another type of rainwater utilization system is provided,which detects both the upper and the lower limits of the water level ofthe storage tank to adjust the water flow in the system. The systemcomprises an initial precipitation collection tank, a purifier includinga filter and a sterilizer, and a storage tank for storing purifiedrainwater, as in the above-mentioned systems. This system also comprisesa first valve for switching the water path between the initialprecipitation collection tank and the purifier, and a second valveprovided to a tap-water supply pipe extending from the storage tank. Anupper limit level sensor is connected to the first valve, and a lowerlimit level sensor is connected to the second valve. If the upper limitlevel sensor detects that the water level of the storage tank hasreached the prescribed upper limit, it causes the first valve to switchthe water path from the purifier to the initial precipitation collectiontank. Upon switching the water path, the rainwater collected from theroof flows into the initial precipitation collection tank, and no morerainwater flows into the purifier. If the lower limit level sensordetects that the water level of the storage tank has reached theprescribed lower limit, it causes the second valve to open in order tosupply the tap water into the storage tank. By filling the storage tank,which is short of water, with the tap water, the water level of thestorage tank is kept at a desired level. In the above-described systems,the initial precipitation collection tank may have a timer and adrainage valve in order to drain the initial portion of rainfall awayfrom the tank after a prescribed time period.

[0024] Preferably, the filter has a physical filtration screen forfiltering the rainwater collected from the roof, and a pH-adjustingagent for adjusting the pH value of the rainwater for neutralizationbecause the collected rainwater is generally acidic. The sterilizercontains aqueous hydrogen peroxide and a primary reactive catalyst inorder to produce active oxygen species (i.e., free radicals) throughdecomposition of the hydrogen peroxide. The active oxygen species areused to sterilize the filtered rainwater.

[0025] The storage tank contains a secondary reactive catalyst thatreacts with the active oxygen species (i.e., free radicals) remaining inthe purified rainwater supplied from the purifier, and that decomposesor eliminates the residual active oxygen species. In the reaction, thesecondary reactive catalyst decomposes organic substances, whileproducing oxygen.

[0026] Preferably, the storage tank consists of multiple interconnectedunits or barrels. The number of units is selected depending on how muchpurified water is required to be stored. The storage tank is placed inthe basement or buried in the ground.

[0027] In the system that has both upper and lower limit level sensors,a back-up sensor is further furnished to the system. The back-up sensoris placed slightly higher than the upper limit level sensor, and isconnected to both the switching valve (i.e., the first valve) and thetap-water supply valve (i.e., the second valve). If the upper limitlevel sensor is out of order, the back-up sensor detects the water levelof the storage tank, and carries out the same operations as the upperlimit level sensor Namely, the back-up sensor causes the switching valveto shut off the water path to the purifier, and allows the rainwater toflow into the initial precipitation collection tank.

[0028] The upper limit level sensor is also connected to the tap-watersupply valve. When the tap water is supplied to the storage tank becauseof the shortage of the purified rainwater, the upper limit level sensordetects the elevating water level, and causes the tap-water supply valveto close when the water level reaches the upper limit. As was mentionedabove, if the upper limit level sensor is out of order, the back-upsensor detects the elevating water level, and causes the tap-watersupply valve to close. In this manner, the water level of the storagetank is kept in the desirable range.

[0029] The system has a pump for pumping the purified rainwater from thestorage tank for various uses. Preferably, an activated charcoal filterand a sediment filter are provided at or after the outlet port of thestorage so that the purified rainwater is further filtered before beingused indoor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Other objectives and advantages will be apparent from thefollowing detailed description of the invention in conjunction with theattached drawings, in which:

[0031]FIG. 1 schematically illustrates an example of rainwaterutilization system according to the invention;

[0032]FIG. 2 schematically illustrates the water collecting containerand the initial water tank used in the system shown in FIG. 1;

[0033]FIG. 3 schematically illustrates the essential portions of thesystem shown in FIG. 1;

[0034]FIG. 4 illustrates another structure of the essential portions ofthe system shown in FIG. 1;

[0035]FIG. 5 schematically illustrates an example of the purifier of thesystem shown in FIG. 1;

[0036]FIG. 6 illustrates an example of storage tanks used in the systemshown in FIG. 1;

[0037]FIG. 7 illustrates an operation flow for removing a predeterminedamount of initial precipitation;

[0038]FIG. 8 illustrates an operation flow of purification of rainwater;and

[0039]FIG. 9 illustrates an operation flow of supplying purified waterfrom the storage tank.

DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS

[0040] The preferred embodiments of the invention will now be describedin detail with reference to the drawings.

[0041]FIG. 1 illustrates the overall structure of rainwater utilizationsystem 1 of the invention, which is applied to a residential building.The system treats the rainwater that has fallen on the building so thatit rainwater becomes suitable for both outdoor and indoor use. Outdooruse includes watering garden plants, washing cars, and other incidentaltasks. Indoor use includes bathroom, laundry, sanitary, and kitchenpurposes.

[0042] The rainwater falling on roof 2 flows into gutter 3, and iscollected in the container 10 placed under the eaves. A strainer 11 isfurnished in the container 10. An initial pipe 12 extends from container10 to initial precipitation collection tank 20, and is equipped with aswitching valve 15. The initial precipitation collection tank 20 and theswitching valve 15 are provided for purposes of separating apredetermined quantity of initial precipitation from the rainwatercollected from the roof 2. In other words, the initial precipitationcollection tank 20 is adapted to receive and temporarily store only theinitial portion of rainfall via the switching valve 15, which is open inorder to remove the initial precipitation.

[0043]FIG. 2 illustrates a detailed view of the initial precipitationcollection tank 20 and the switching valve 15. The initial precipitationcollection tank 20 has a capacity of storing a predetermined quantity ofrainwater, dependent on the roof surface area. The capacity can be, forexample, 200 to 500 liters, or alternatively, the first 2 mm to 3 mm ofprecipitation depending on the area of the roof 2. The switching valve15 is open when the initial portion of rainfall is guided into theinitial precipitation collection tank 20 from the container 10. A levelsensor 21 is furnished to the initial precipitation collection tank 20,and is connected to the switching valve 15. If the level sensor detectsthat the water level of the initial precipitation collection tank 20 hasreached the prescribed level, it causes the switching valve 15 to closeup and prevents the rainwater from flowing into the initialprecipitation collection tank 20. Preferably, the switching valve 15 iscontrolled so that it automatically opens if a failure occurs to thesystem in order to guide the rainwater into-the tank 20 and drain fromthe system without fail.

[0044] The initial precipitation collection tank 20 is furnished with atimer 22 and a drainage valve 23. The timer 22 is activated when thelevel sensor 21 detects that water level of the initial precipitationcollection tank 20 has reached the predetermined level. After a presettime period (e.g., 10 hours to 120 hours), the drainage valve 23 opensto drain the initial precipitation from the initial precipitationcollection tank 20 in preparation for the next rainfall. The initialprecipitation collection tank 20 is also furnished with an overflow pipe24 and a hand-powered valve 25 for manual drain.

[0045] As illustrated in FIG. 1, the initial portion of rainwatertemporarily stored in the initial precipitation collection tank 20 canbe recycled into a biotope or infiltration trench in the garden or thebackyard,

[0046]FIGS. 3 and 4 illustrate how the rainwater is guided to purifier30 and storage tank 60. In the example shown in FIG. 3, an inlet tube 16is bypassed from the initial pipe 12, and leads to the purifier 30. Whenthe switching valve 15 closes up, the subsequent rainwater collected inthe container 10 is allowed to enter the purifier 30. The purifier 30 isa two-stage purification system, and comprises of a filtering tank 40and a sterilization tank 50. The inlet port of the filtering tank 40 ispositioned higher than the outlet port in order to guarantee one-wayflow into the sterilization tank 50.

[0047] The example illustrated in FIG. 4 uses a strainer 115 in theinitial container. The strainer 115 has a tilted surface with respect tothe direction of the rainfall. The tilted surface of the strainer 115is, for example, a metallic mesh. At the beginning of rainfall or if therain slackens, the raindrops flow along the tilted surface of thestrainer 115, and are collected in the initial precipitation collectiontank 20. If the rain becomes heavier, the raindrops penetrate thestrainer 115, and flow into the purifier 30. In this example, a manuallyoperated valves 55 and an overflow outlet port are furnished between thepurifier and the storage tank, so that if the water level of the storagetank reaches the upper limit, the valve 55 is closed manually, whileexcessive rainwater is drained. The valve 55 may be positioned beforethe purifier 30.

[0048]FIG. 5 illustrates the detailed structure of the purifier 30. Thefiltering tank 40 is furnished with a metallic screen 41 having a numberof holes with a diameter of, for example, 0.75 mm, and a pH-adjustingagent 42. The metallic screen 41 physically filters the rainwatersupplied from the inlet pipe 16. The pH-adjusting agent 42 is placed onthe bottom of the filtering tank 40 in order to neutralize therainwater. Rainwater is generally acidic with a pH value of about 4.6.The pH-adjusting agent 42 is, for example, CaCO₃, which brings the pHvalue of the rainwater to about 6.

[0049] The sterilization tank 50 sterilizes the filtered rainwater usingactive oxygen species (or free radicals) produced by the decompositionof hydrogen peroxide (H₂O₂). Aqueous hydrogen peroxide is contained in asupply tank 51, which is connected to the sterilization tank 50. Solidcatalyst grains are put into the supply tank 51, and start reacting withthe hydrogen peroxide (H₂O₂) to produce pure oxygen (O₂). This oxygengenerates pressure, and pushes the hydrogen peroxide (H₂O₂) out of thesupply tank 51. The hydrogen peroxide is constantly supplied to thesterilization tank 50 via a tube coupled with a primary reactivecatalyst 52 placed on the bottom of the sterilization tank 50. Thehydrogen peroxide reacts with the primary reactive catalyst 52, andproduces active oxygen species (or free radicals). During this reaction,oxygen is also produced because the active oxygen species turn intooxygen in a short time. The produced oxygen balances with the pressurefrom the supply tank 51. The primary reactive catalyst 52 is, forexample, annealed MnO₂.

[0050] In this manner, hydrogen peroxide is constantly supplied from thesupply tank 51 to the primary reactive catalyst 52 under a pressurebalance between the oxygen produced in the supply tank 51 and the oxygengenerated from the primary reactive catalyst 52. The reaction rate, andthe quantities and percentages of the produced active oxygen species(e.g., hydroxyl radical (•OH⁻), superoxide anion radical (•O₂ ⁻),peroxide(•O₂ ²⁻)) are determined by the quantitative ratio of thehydrogen peroxide supplied to the sterilization tank 50 to the primaryreactive catalyst 52, the concentration of the aqueous hydrogenperoxide, the water temperature, and other factors.

[0051] Among the active oxygen species, peroxide(•O₂ ²⁻) has a highsterilization effect. The superoxide anion radical (•O₂ ⁻) coagulatesheavy metal ions, and the hydroxyl radical (•OH⁻) decomposes organicsubstances. Although most of these active oxygen species turn into anoxygen molecule (O₂) in a short time, a certain quantity of activeoxygen species remain in the rainwater.

[0052]FIG. 6 illustrates the storage tank 60, which receives thepurified rainwater from the purifier 30. The storage tank 60 may beconsist of interconnected multiple units (e.g., barrels or tanks),depending on how much purified rainwater is to be stored. Preferably,the storage tank 60 is placed in a basement or buried under the ground.Each storage tank 60 contains a secondary reactive catalyst 61, whichpromotes the decomposition and elimination of the residual active oxygenspecies remaining in the purified rainwater. During the reaction betweenthe secondary reactive catalyst 61 and the residual active oxygenspecies, oxygen is produced and organic substances are decomposed, andconvection is caused in the storage tank 60. The convection occursbecause of the decomposition of the residual active oxygen species bythe secondary reactive catalyst 61, which allows the purified rainwaterto be kept clean and pure in the storage tank 60 for a long time,without deterioration.

[0053] The last container of storage tank 60 is furnished with an upperlimit level sensor 62 and a lower limit level sensor 63. A back-upsensor 64 is also provided adjacent to or slightly higher than the upperlimit level sensor 62. The upper limit level sensor is connected to andcooperates with the switching valve 15. If the water level of thestorage tank 60 has risen up to the prescribed upper limit, the upperlimit level sensor 62 is activated, causing the switching valve 15 toopen in order to allow the rainwater to flow into the initialprecipitation collection tank 20. The lower limit level sensor 63 isconnected to and cooperates with the tap-water supply valve 66. If thewater level of the storage tank 60 has fallen to the lower limit (whichmeans that the quantity of rainwater stored in the storage tank hasbecome the minimum acceptable amount), the lower limit level sensor 63is activated, and the tap-water supply valve 66 is opened. Consequently,a required quantity of tap water is supplied into the storage tank 60.

[0054] The upper limit level sensor 62 is also connected to thetap-water supply valve 66. If the upper limit level sensor 62 detectsthat the water level has risen to the upper limit due to thesupplemental tap water, it causes the tap-water supply valve 66 to closeup so as not to supply the tap water into the storage tank any more.

[0055] The back-up sensor 64 is used if the upper limit level sensor 62is out of order. The back-up sensor 64 guarantees the operations of thesystem and prevents undesirable accidents. If the upper limit levelsensor 62 can not detect the water level of the storage tank for somereasons, the back-up sensor 63 in turn detects the water level as havingreached the upper limit. Then, the back-up sensor 63 causes theswitching valve 15 to open, or the tap-water supply valve 66 to close.

[0056] Preferably, an overflow port 67 is provided to the upper portionof the storage tank 60 to drain the excessive rainwater out of thestorage tank 60.

[0057] In the preferred embodiment of the system 1, a pump 70 isprovided to pump the purified rainwater from the storage tank 60 forindoor use. Preferably, a filter 80, which consists of an activatedcarbon filter 81 and sediment filter 82, is provided after the pump 70.The activated carbon filter 81 is, for example, a commercially available20-inch filter for removing positive ions and the like. The sedimentfilter 82 is, for example, a 5 μm filter for removing solutes other thanions.

[0058] Although, in FIG. 6, indoor use is exemplified as sanitary use,the purified and charcoal-filtered rainwater, which is purer and saferthan the tap water, may be used for drinking, cooking, and other kitchenuse.

[0059]FIGS. 7 through 9 illustrate the operational flows of therainwater utilization system shown in FIGS. 1 through 6.

[0060] When rainfall begins, the rainwater flows along the roof surface2 and the gutter3, and is collected in the container 10 placed under theeaves. The rainwater further flows through the initial pipe 12 and iscollected in the initial precipitation collection tank 20 through theswitching valve 15 that is in the open state (step S1).

[0061] In step S2, it is determined whether the level sensor furnishedto the initial precipitation collection tank 20 has been activated. Ifthe water level of the initial precipitation collection tank 20 reachesthe predetermined level that corresponds to a specified quantity ofrainwater, for example, precipitation of 2 to 3 mm, the level sensor 21is activated.

[0062] Then, a signal is supplied to the switching valve 15, causing itto close up so as to allow the rainwater to flow into the purifier. Atthe same time, the timer 22 is activated (step S3).

[0063] When a predetermined time period has elapsed (YES in step S4),the drainage valve 23 of the initial precipitation collection tank 20 isopened (step S5), and the temporarily stored initial rainwater isdrained out of the tank 20 (step S6).

[0064]FIG. 8 illustrates the operational flow of the purification andstorage of rainwater, which continues from step S3 of FIG. 7. Uponclosing the switching valve 15, the rainwater collected in the container10 is allowed to flow into the purifier 30 (step S11).

[0065] The rainwater supplied to the purifier 30 is physically filtratedby the metallic screen 41 (step S12). Then, the filtered rainwater isneutralized by a pH adjusting agent 42 placed on the bottom of thefiltering tank (step S13).

[0066] The pH-adjusted rainwater is then supplied to the sterilizingtank 50 of the purifier 30, in which sterilization is carried out usingactive oxygen species produced by the decomposition of aqueous hydrogenperoxide (H₂O₂) (step S14).

[0067] The sterilized rainwater is supplied to the storage tank 60 (stepS15), in which the residual active oxygen species remaining in thesterilized rainwater are decomposed and eliminated using secondaryreactive catalyst 61 (step S16). The reaction between the secondaryactive catalyst 61 and the residual active oxygen species produceoxygen, while decomposing the organic substances contained in therainwater. For this reason, the rainwater stored in the storage tank 60does not deteriorate for a long time, and can be maintained clean andpure.

[0068] In step S17, it is determined whether the water level of thestorage tank 60 has reached the prescribed upper limit. If the waterlevel has risen to the upper limit, the upper limit level sensor 62 isactivated (YES in step S17).

[0069] The activation of the upper limit level sensor 62 causes theswitching valve 15 to open in order to allow the rainwater to flow intothe initial precipitation collection tank 20.

[0070] If the upper limit level sensor was not activated for somereasons (NO in step S17), in spite of the increase in water level, it isthen determined whether the back-up sensor 64 has been activated (stepS18). If the back-up sensor 64 has been activated (YES in step S18), theswitching valve 15, which is connected to the back-up sensor 64, isopened to allow the rainwater collected in the container 10 to pass intothe initial precipitation collection tank 20 (step S19). In this manner,even if the upper limit level sensor 62 does not work for some reason,the back-up sensor 64 carries out the required operations in place ofthe upper limit level sensor 62, thereby guaranteeing the operations ofthe system 1.

[0071] As illustrated in FIG. 1, the rainwater flowing into the initialprecipitation collection tank 20 can be recycled as irrigation forbiotope or green field.

[0072]FIG. 9 illustrates the operational flow of supplying the tap waterinto the storage tank 60 in times of a shortage of stored rainwater. Asthe purified rainwater is being used for various purposes, the quantityof the stored rainwater decreases, and the water level of the lastcontainer of storage tank 60 may reach the lower limit (i.e., theminimum level), especially in a dry season. The system 1 of the presentinvention detects a shortage of the purified rainwater, and supplies thetap water in order to maintain the water level of the storage tank 20 ata desirable level.

[0073] First, it is determined whether the lower limit level sensor 63has been activated (step S21). If the water level of the storage tank 60has reached the lower limit, the lower limit level sensor 63 is turnedon (YES in step S21). The activation of the lower limit level sensor 63causes the tap-water supply valve 66, which is connected to andcooperates with the lower limit level sensor 63, to open (step S22).Then, a required quantity of tap water is supplied to the storage tank60 (step S23).

[0074] If, due to the supply of the tap water, the water level of thestorage tank 60 returns to the upper limit, the upper limit level sensor62 detects the water level as having reached the upper level, and causesthe tap-water supply valve 66 to close. This automatic closing of thetap-water supply valve 66 is monitored (step S24). If the tap-watersupply valve 66 was not closed for some reason (NO in step S24), whichmeans that the upper limit level sensor 62 did not work, the processproceeds to step S25, in which it is determined whether the back-upsensor 64 is activated. If the back-up sensor 64 has been activated (YESin step S25), the tap-water supply valve 66 is shut to prevent the tapwater from entering the storage tank any more (step S26).

[0075] Although not illustrated in the drawings, either a control boardor a computer program can control these operations.

[0076] The purified rainwater stored in the storage tank 60 is pumped upfor various uses. Although the purified rainwater can be used as it isbecause of its purity and cleanliness, it may be filtered further beforeit is used for kitchen purposes. For example, an activated carbon filter81 can be used to remove positive ions and the like, and a sedimentfilter 82 can be used to remove solutes other than ions. The activatedcarbon filter and the sediment filter can be used in combination.

[0077] The rainwater utilization system has various applications in awide range of scales. Such applications include, but not limited to:

[0078] (1) supplying household water for washing cars, sprinkling,watering garden plants (small scale);

[0079] (2) supplying sanitary water used in bath rooms and for laundry(small or medium scale);

[0080] (3) supplying water to a pond or biotope (in a small scale);

[0081] (4) using rainwater as coolant in an air conditioning system or aheat exchanger (medium or large scale);

[0082] (5) supplying living water used in a daily life for laundry,bathroom, and cleaning (medium scale);

[0083] (6) supplying kitchen water for drinking, cooking, dish washer,etc. (medium scale);

[0084] (7) recycling rainwater in a hot-water system or a solar heatersystem (medium scale);

[0085] (8) recycling rainwater for sprinkling kitchen gardens and greenhouse (wide range of scales);

[0086] (9) watering potted plants or house plants (small or mediumscale);

[0087] (10) storing purified rainwater as emergency water life line as aprecaution for natural calamities (medium or large scale);

[0088] (11) using rainwater for fire fighting (large scale);

[0089] (12) as a measure against water shortage (e.g., an infiltrationtrench for garden trees and plants, permeable water for preventing thelowering of groundwater levels, etc. wide-ranging scales); and

[0090] (13) as a measure against flood (including infiltration trenchesand reservoirs for urban systems) (medium or large scale).

[0091] In the above applications, the rainwater drained from the initialprecipitation collection tank or overflowing the storage tank isrecycled for outdoor uses. On the other hand, the purified rainwaterthrough pH adjustment and sterilization is suitable for indoor uses. Inthis manner, the invention can make best use of natural resources,positively utilizing rainwater.

[0092] Although the invention has been described based on the preferredembodiments, the invention is not limited to these examples and manychanges and substitutions are possible without departing from the scopeof the invention, which is defined by the appended claims.

What is claimed is:
 1. A method for utilizing rainwater falling on abuilding, comprising the steps of: removing a predetermined quantity ofinitial precipitation from the rainwater collected from the roof surfaceof the building; supplying the subsequent rainwater to a purifier tocarry out pH adjustment and sterilization; supplying the purifiedrainwater to a storage tank; and pumping out the purified rainwater fromthe storage tank for various uses.
 2. The method of claim 1, furthercomprising the step of carrying out physical filtration at or before aninlet port of the purifier.
 3. The method of claim 1, wherein the pHadjustment neutralizes the rainwater that is acidic, and thesterilization is carried out using active oxygen species produced bydecomposition of aqueous hydrogen peroxide.
 4. The method of claim 1,further comprising the step of decomposing and eliminating residualactive oxygen species remaining in the purified rainwater that has beensupplied to the storage tank.
 5. A method for utilizing rainwaterfalling on a building, comprising the steps of: removing a predeterminedquantity of initial precipitation from the rainwater collected from theroof surface of the building; supplying the subsequent rainwater to apurifier to carry out pH adjustment and sterilization; supplying thepurified rainwater to a storage tank; and monitoring the water level ofthe storage tank, and preventing the rainwater from entering thepurifier and the storage tank if the water level has reached apredetermined upper limit.
 6. The method of claim 5, further comprisingthe step of carrying out physical filtration at or before an inlet portof the purifier.
 7. The method of claim 5, wherein the pH adjustmentneutralizes the rainwater that is acidic, and the sterilization iscarried out using active oxygen species produced by decomposition ofaqueous hydrogen peroxide.
 8. The method of claim 5, further comprisingthe step of decomposing and eliminating residual active oxygen speciesremaining in the purified rainwater that has been supplied to thestorage tank.
 9. A method for utilizing rainwater falling on a building,comprising the steps of: removing a predetermined quantity of initialprecipitation from the rainwater collected from the roof surface of thebuilding; supplying the subsequent rainwater to a purifier to carry outpH adjustment and sterilization; supplying the purified rainwater to astorage tank; and monitoring the water level of the storage tank, andsupplying tap water into the storage tank if the water level of thestorage tank has reached a predetermined lower limit.
 10. The method ofclaim 9, further comprising the step of carrying out physical filtrationat or before an inlet port of the purifier.
 11. The method of claim 9,wherein the pH adjustment neutralizes the rainwater that is acidic, andthe sterilization is carried out using active oxygen species produced bydecomposition of aqueous hydrogen peroxide.
 12. The method of claim 9,further comprising the step of decomposing and eliminating residualactive oxygen species remaining in the purified rainwater that has beensupplied to the storage tank.
 13. A method for utilizing rainwaterfalling on a building, comprising the steps of: removing a predeterminedquantity of initial precipitation from the rainwater collected from theroof surface of the building; supplying the subsequent rainwater to apurifier to carry out pH adjustment and sterilization; supplying thepurified rainwater to a storage tank; monitoring the water level of thestorage tank, and preventing the rainwater from entering the purifierand the storage tank if the water level of the storage tank has reacheda predetermined upper limit; supplying tap water into the storage tankif the water level of the storage tank has reached a predetermined apredetermined lower limit; and pumping out the purified rainwater fromthe storage tank for various uses.
 14. The method of claim 13, furthercomprising the step of carrying out physical filtration at or before aninlet port of the purifier.
 15. The method of claim 13, wherein the pHadjustment neutralizes the rainwater that is acidic, and thesterilization is carried out using active oxygen species produced bydecomposition of aqueous hydrogen peroxide.
 16. The method of claim 13,further comprising the step of decomposing and eliminating residualactive oxygen species remaining in the purified rainwater that has beensupplied to the storage tank.